The invention described herein was made in the course of work under a grant or award from the United States National Science Foundation.
U.S. Pat. No. 3,741,809, issued June 26, 1973, to M. Anbar (herein the "Anbar" patent), discloses a method and apparatus for the pollution-free generation of electrochemical energy from coal or other carbonaceous fuels. The process there disclosed is a cyclical one in which a metal of the group consisting of lead, bismuth and antimony is first oxidized with oxygen at high temperatures in an electrochemical cell containing a molten salt electrolyte, the cell being one wherein said metal is the anode and oxygen is supplied at the cathode. The resultant oxidation of the metal generates the electromotive force. The formed metal oxide, e.g., PbO, is taken up by the molten salt and carried to an adjacent regeneration chamber to which carbonaceous fuel is supplied to reduce the metal oxide back to the form of metal which separates in molten form from the molten salt and is returned to the electrochemical cell to continue the cycle. While a practice of the method disclosed in the Anbar patent will theoretically produce an open cell voltage of approximately 0.76 volt at 450.degree. C or 0.7 volt at the more efficient operating temperature of 600.degree. C, the effective, or load voltage which can be obtained therefrom as a practical matter at 600.degree. C does not exceed about 0.5 volt or about 0.4 volt at 800.degree. C. The invention disclosed in the Anbar patent is assigned to the assignee of the present invention, and the subject matter of the said patent is specifically incorporated herein, by reference, for background information.
It is an object of this invention to provide a method and apparatus which, while utilizing the electrochemical cell of the Anbar patent, is nevertheless capable of providing much higher open circuit and operating voltages. A more particular object is to provide a cell structure which eliminates the necessity for material transport from the regeneration reactor to the electrochemical cell and vice versa.
It will be observed that in the simple metal-air cell disclosed by Anbar the voltage is necessarily limited to that provided by the free energy of formation of the metal oxide, e.g., PbO, at unit activity. The free energy released by subsequent chemical reduction of the metal oxide is not available as electric power. It is a further object of this invention to provide a method and apparatus wherein both the free energy of formation of the metal oxide and the free energy released by chemical reduction of said oxide become available as electric power, the resulting voltage tending to assume a higher value as determined by the more negative free energy of formation of carbon dioxide.